The presents a study of the lexical units of the language of the specialty “Hydrotechnikal Сonstruction” based on a selection of dictionaries, textbooks, articles, regulations and scientific and journalistic texts. There is analysis of concepts of term, terminological field, terminological system, core and their interpretation in the scientific literature. The purpose of the study is to propose a thematic and derivational classification of hydrotechical terms to build a model of a terminological system. The multidimensionality of the hydrotechnical profile, including construction, hydrology and ecology, as well as related to biology, hydropower generation, navigation, agriculture and other branches of scientific and practical activity, is noted. In this regard, a horizontal structure of the terminological fields of the hydrotechnical system is proposed; the set of lexical units of the language of the specialty “hydraulic engineering” is considered as an ordered terminological system with a multi-core structure. The polycentricity of the system of hydrotechnical terms and the difusseness of its constituent microfields has been proved using a quantitative method. The novelty of the study is caused by the specifics of the material, which has been little studied so far, as well as the approach to its systematization. Observation of the hydrotechnical vocabulary made it possible to put forward a hypothesis about the relatively small number of borrowings in its corpus, which in turn determines the ambivalent nature of many hydrotechnical terms and the diffuseness of the microfields that form the terminological system. The study of hydrotechnical terms showed that the process of formation of terminological units can take place in a different sequence: from word to term or from term to word. Moreover, along with the term, its etymon can continue to be used in the general literary language. Derivation is active; however, the borrowing of terms is not the main source of replenishment of hydrotechnical terminology. The conclusions are drawn about the special structure of the terminological system, which reflects the multidimensional nature of. The Hydrotechnikal Сonstruction”, polycentric nature of the hydrotechnical terminological system, which includes intersecting term fields, is explained by the history of the industry and inter-industry relations. The results are necessary for the preparation of a manual for foreigners studying this discipline in Russian, which represents the relevance and practical significance of the study.